Segmented mixing device for jet engines

ABSTRACT

Disclosed is a means for reducing jet engine exhaust noise wherein mixing is enhanced between adjacent exhaust flows and between exhaust flow and free-stream flow. The device does so with a very small degradation in aircraft performance. The device is a segmented, triangular or trapezoidal shaped, curved extension to a nozzle&#39;s sleeve that results in a serrated trailing edge. The nozzle extensions enhance the natural free mixing of the jet&#39;s exhaust flows and therefore reduce the acoustic energy associated with the velocity differences between the streams in which they are imbedded. The novel structure forces adjacent flows to penetrate into one another to a greater depth than that achievable with free mixing and results in a more uniform flow in a shorter stream wise distance.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from provisional applicationserial No. 60/203,222, filed May 5, 2000.

FIELD OF THE INVENTION

[0002] Jet engines can produce a high noise level if the velocity of themass flow exiting the engine is non-uniform and high. For performanceconsiderations, jet engines often have multiple nozzles with the massflow exiting each nozzle at a different velocity. Since noise radiatingfrom a jet's exhaust increases with the intensity and non-uniformity ofthe exhaust velocity, jet noise reduction concepts have historicallyfocused on methods for rapidly mixing the flows and achieving a uniformvelocity within a short distance of the nozzles.

BACKGROUND OF THE INVENTION

[0003] Various flow-mixing devices have been employed in the past toachieve a uniform velocity within a jet's exhaust and to reduce thenoise radiated from the exhaust flow. While those devices have beensuccessful at reducing jet noise, the thrust, drag, and weight penaltyassociated with those devices have often been of a magnitude that thenoise at constant aircraft performance has not been reduced. During theNASA Advanced Subsonic Transport (AST) Program (reference 1) sharppointed, triangular shaped, extensions added to the sleeve of anexternal plug primary nozzle were tested and were found to reduce jetnoise. A. D. Young et al (U.S. Pat. No. 3,153,319, reference 2) alsodeveloped extensions that when added to the trailing edge of nozzlesreduced jet noise.

[0004] The primary difference between the above-described prior art andthe hereinafter described invention is the rounding of the upstreamintersection of the extensions with the nozzle and the rounding of theextension's trailing edge. Rounding has been found to enhance thereduction of low frequency noise while inhibiting an increase in highfrequency noise. Increased high frequency noise has been acharacteristic of the previous sharp edged devices even though they havereduced low frequency noise and have had a net acoustic benefit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0005]FIG. 1 is a perspective view of a jet engine segmented mixingdevice with internal plug nacelle;

[0006]FIG. 2 is illustrative of a jet engine segmented mixing devicewith internal plug nacelle;

[0007]FIG. 3 is an aircraft jet engine segmented mixing device withmixed flow nacelle;

[0008]FIG. 4 is a semi-round tip triangular planform showing of asegmented mixing device nozzle sleeve;

[0009]FIG. 4A is a sectional view taken along the lines A-A of FIG. 4showing in more detail how the outer surface of the mixing deviceextensions curve inward towards the engine center line;

[0010]FIG. 4B is a sectional view taken along the lines B-B of FIG. 4showing in more detail how the extensions having a planform shape createa streamwise vortex;

[0011]FIG. 5 is further illustrative of the present trapezoidal planformnozzle sleeve; and,

[0012]FIG. 5A is illustrative of streamwise vortex flow.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention comprises a segmented mixing device which,when applied to the nozzle of a jet engine, enhances mixing betweenadjacent flows and reduces the noise radiated from the jet's exhaustflow. The device does so with a very small degradation in aircraftperformance. The mixing device is a segmented, triangular or trapezoidalshaped, curved extension 1 to a nozzle's sleeve which results in aserrated trailing edge (see FIGS. 1, 2, and 3). This inventioncomprises: 1) A modification from the sharp pointed, triangular shaped,nozzle extensions evaluated in the hereinafter referenced NASA ASTprogram to a semi-round, triangular or trapezoidal shaped planform (seeFIGS. 4 and 5). 2) An application of the present nozzle extensions tointernal and external plug primary nozzles of dual flow exhaust systems(see FIGS. 1 and 2). 3) An application of the nozzle extensions tosecondary nozzles of dual flow exhaust systems (see FIGS. 1 and 2). 4)An application of the nozzle extensions to the nozzle of mixed flowexhaust systems and the flow splitter between the primary and secondarystreams of those systems (see FIG. 3). And, 5) an application of thenozzle extensions to the trailing edge of any surface separatingadjacent flows wherein enhanced mixing is desired.

[0014] The purpose of the present nozzle extensions 1 is to enhance thenatural free mixing of the exhaust flows and to reduce the acousticenergy associated with the velocity differences between the streams inwhich they are imbedded. The presently configured nozzle extensionsenhance the natural free mixing between adjacent streams by forcing theadjacent flows to penetrate into one another to a greater depth thanthat achievable with free mixing and therefore results in a more uniformflow in a shorter stream wise distance. The acoustic benefit of theextensions increases as the velocity differences between the streamsincrease. Two methodologies are employed to enhance mixing: 1) The outersurface of the extensions curve inward towards the engine centerlineforcing the secondary (outer) flow into the primary (inner) flow (seeFIG. 4, sec A-A). 2) The extensions have a planform shape that creates astream wise vortex that also enhances rapid mixing of the two streams(see FIG. 4, sec B-B and FIG. 5). Outward turned segments can also beused to enhance mixing. However, the thrust losses for outward turnedsegments has been greater than for inward turned segments. The presentconcept however includes rounding to outward turned segments.

[0015] Unlike the previous NASA AST configurations and the A. D. Younget al configurations described in U.S. Pat. No. 3,153,319, theextensions defined herein incorporate a planform with semi-roundedintersections with the baseline nozzle and semi-round trailing edges.The purpose of the upstream rounding is to increase the strength of thestream wise vortex by allowing the primary (inner) flow to exit thenozzle sooner and in a more radial manner. Rounding the upstreamintersection also eliminates the stress concentrations and low fatiguelife of the previous NASA AST and A. D. Young et al concepts. Roundingthe extension's trailing edge separates the two stream wise vortexes andincreases the circumferential surface area available for the secondary(outer) flow to penetrate the primary (inner) flow. In addition,rounding the trailing edge increases the average turning angle of thesecondary flow resulting in greater penetration of the secondary flowinto the primary flow and increased mixing of the two flows. Roundinghas been found to enhance the reduction of low frequency noise whileinhibiting an increase in high frequency noise. The increase in highfrequency noise has been a characteristic of the previous designs. Thenozzle extensions may vary in length, width, curvature, and count beingonly constrained by the geometry of the baseline nozzle.

References

[0016] 1. D. C. Kenzakowski, J. Shipman, S. M. Dash, J. E. Bridges, andN. H. Saiyed, AIAA-2000-0219, “Turbulence Model Study of Laboratory Jetswith Mixing Enhancements for Noise Reduction”, January 2000.

[0017] 2. A. D. Young et al, U.S. Pat. No. 3,153,319, “Jet NoiseSuppression Means”, Oct. 20, 1964.

What is claimed is:
 1. A segmented mixing device for jet enginescomprising a segmented, triangular or trapezoidal shaped, curvedextension of a nozzle sleeve wherein the plan view of said nozzleextension comprises a sinusoidal or “saw toothed” wave shape.
 2. Anozzle extension for a jet engine having a planform with semi-roundintersections with the baseline nozzle and semi-round trailing edges. 3.A nozzle extension for a jet engine, said nozzle extension having anouter surface curving inward, toward the engine centerline, therebyforcing the outer flow into the inner flow, and, said nozzle extensionhaving a planform shape which creates a stream wise vortex therebyenhancing rapid mixing of the outer flow and the inner flow.
 4. A nozzleextension for a jet engine, said nozzle extension having an outersurface curving outward, away from the engine centerline, therebyforcing the inner flow into the outer flow, and, said nozzle extensionhaving a planform shape which creates a stream wise vortex therebyenhancing rapid mixing of the outer flow and the inner flow.
 5. A nozzleextension according to claims 2, 3 or 4 utilized on the internal orexternal plug primary nozzle and the secondary nozzle of dual flowexhaust systems.
 6. A nozzle extension according to claims 2, 3 or 4utilized on the nozzle of a mixed flow exhaust system and the flowsplitter between the primary and secondary stream of those systems.
 7. Asurface separating adjacent flows, said surface having semi-roundtrailing edges for providing enhanced mixing.
 8. A method for enhancingnatural free mixing between adjacent streams of gases by forcingadjacent streams of gasses to penetrate into one another to a greaterdepth than by free mixing thereby causing a more uniform flow in ashorter streamwise distance.
 9. In combination: a gas flow nozzle; saidgas flow nozzle having a trailing edge; an extension for said gas flownozzle; and, said extension having semi-round tips and valleys forenhancing the reduction of low frequency noise while inhibiting anincrease in high frequency noise.
 10. The combination according to claim9 wherein said extension has a triangular planform.
 11. The combinationaccording to claim 9 wherein said extension has a trapezoidal planform.